Chicago River dyed green for St. Patrick's Day

The Chicago River is dyed green for St. Patrick's Day on Saturday, March 16, 2019 in Chicago. ( James Foster/Chicago Sun-Times via AP)

The Chicago River is dyed green for St. Patrick's Day on Saturday, March 16, 2019 in Chicago. ( James Foster/Chicago Sun-Times via AP)

Photo: James Foster, AP

Photo: James Foster, AP

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The Chicago River is dyed green for St. Patrick's Day on Saturday, March 16, 2019 in Chicago. ( James Foster/Chicago Sun-Times via AP)

The Chicago River is dyed green for St. Patrick's Day on Saturday, March 16, 2019 in Chicago. ( James Foster/Chicago Sun-Times via AP)

Photo: James Foster, AP

Chicago River dyed green for St. Patrick's Day

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CHICAGO (AP) — Thousands of revelers lined the streets to watch the Chicago River be dyed green for St. Patrick's Day.

The annual tradition that dates back decades took place Saturday morning on a stretch of the river in downtown Chicago. Celebrants stood on the Michigan Avenue bridge and the city's riverwalk to watch members of Chicago Plumbers Local 130 dump and spray the dye into the river from boats.

The union says the dye formula is a "closely guarded secret" but members assure that it's been tested and is safe for the environment.

Afterward the city stepped off its annual St. Patrick's Day Parade , one of the biggest parades in the city. Participants in the 64th annual parade include Irish step dancers, bagpipers and marching bands.